[clang] [Clang] Add [[clang::no_specializations]] (PR #101469)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

I went for only adding `[[clang::no_specialization]]` to function templates, since the other cases seem even more unlikely to me and seem to have a higher implementation complexity. Is that OK?

https://github.com/llvm/llvm-project/pull/101469